I've also only managed to get as far as the tip as I do not stretch enough or I just don't have time to practice (also have a gf and she rather do it for me than to see me possibly getting hurt lol). However you can easily get further if you just keep stretching on a regular basis, would help to do some yoga. Also make sure to do it near the end of the day when your body is more lose, in the earlier parts of the day your body is still stiff so that can make it near impossible. Having a smaller stomach is a big part of it as well as having a good sized dick. As far as positions go I would suggest laying on your back with or without a pillow under your neck/head a couple feet away from a wall (head towards wall) and then get your legs up to where you can walk down the wall. Just always make sure you stretch, can't stress that enough.

i can selfsuck but not so deep ( only the tip and depends how flexible am I at the moment ....)
technique? just watch selfsuck videos, do some sterching everyday (yoga really helps) and if you dont have a big belly you'll make it after a while.

When I was younger I managed to get my lips around the head using the legs above my head position and pushing down on my butt. Never as able to cum that way. Did back off and shoot into my mouth a few times.